Influence of photoperiod and temperature on growth, gas exchange, and cold hardiness of yellow cypress stecklings
Yellow cypress (Chamaecyparisnootkatensis (D. Don) Spach) stecklings (rooted cuttings) were acclimated for approximately 8 weeks under one of the following photoperiod–temperature treatments: 18 h/10 °C, 18 h/20 °C, 9 h/10 °C, 9 h/20 °C followed by deacclimation in a common environment of 12 h/20 °C for approximately 6 weeks. During acclimation and deacclimation, steckling morphological development, net photosynthesis, transpiration and leaf conductance, and midday shoot water potential were measured. Hardiness was determined by freeze-induced electrolyte leakage. Shoot growth was reduced more by short photoperiods (9 h) than by cool temperature (10 °C) as were net photosynthesis, stomatal conductance, transpiration, and photosynthetic efficiency. Photoperiod-induced cold hardening of shoots and height growth cessation were reversible in warm temperatures (20 °C) and 12-h days, indicating that hardiness induction treatments had no lasting effects on the growth or cold hardiness of this tree species.